The present invention is related to liquid identification. In particular, the present invention involves methods for marking a liquid and methods and systems for the identification of a liquid using at least one chemical marker.
There is a need for novel markers which are suitable for marking liquids such as petroleum fuels. There is also a need for methods of marking, tagging, or otherwise identifying liquids, and methods for distinguishing such marked liquids from otherwise identical but unmarked liquids.
These needs arise primarily from differing price or tax structures of different fuels or even the same fuel used for different purposes. For example, gasoline used for off-highway, non-vehicular purposes such as mining, lumbering or fishing, is commonly taxed at lower rates than that for highway vehicular use. Further, certain grades of oil are used interchangeably for heating oil or for diesel motor fuel. These situations can lead to abuse of the tax laws and cheating by unscrupulous persons.
It is, of course, necessary that the added chemical marker be capable of quick and relatively simple identification by non-scientific personnel. In other instances and aside from tax matters, there are occasions when it is desirable to mark a particular production batch of fuel or solvent to prove the origin of the material. As is readily apparent, any marker so used must be added in small concentration, should not affect the physical or chemical properties of the substances to which it is added and should be easily identified by relatively quick and simple means.
It is desirable to have simple, rapid and sensitive methods to detect the presence of one petroleum product in another. Fuels are sometimes mixed for the purpose of adulterating a higher priced product with a lower priced material, such as the addition of regular grade gasoline to premium gasoline, or for the purpose of evading taxation by the addition of low-taxed light heating oil to highly taxed diesel fuel. Other reasons for identifying particular fuels are determination of theft, or locating leaks from storage facilities at service stations, oil terminals, large scale industrial lubrication systems, or automotive transmission and hydraulic systems.
Thus, chemical markers are often added to a petroleum product to identify the product for a variety of reasons. Markers are used to differentiate among various grades of fuel. For example, markers are used to distinguish premium from regular grade gasolines, or aviation gasoline from motor gasoline. Markers are also widely employed to identify proprietary or specific brands of fuel from a particular refiner. Further, markers are sometimes required by government regulation to monitor the tax classification of diesel fuel, home heating oil, and kerosenes; in the case of tax classification monitoring, markers are used for the identification of petroleum products that might be substituted illegally for more costly or higher taxed fuels.
Most fuel markers are characterized by several important chemical properties. They are miscible in fuel, difficult to remove from the product by any simple treatment (e.g. filtering, bleaching, reactive conversion in the fuel), easily identifiable and, in some cases, quantifiable by the user. Further, for both cost and fuel performance reasons, markers are usually deployed in low concentrations, e.g., in the parts per million (volume/volume) range, and must be effective in their role as product identifiers at such low concentrations.
Markers are often organic dyes, materials with strong absorbency in the visible portion of the electromagnetic spectrum. Thus, a fuel containing such organic dyes immediately provides information to an observer. The red dye, Red-26, is an example of such a marker. Red-26 is used by the IRS to distinguish nontaxed home heating oil in the US from other taxed fuels of similar composition. If red dye is present, no federal taxes have been paid on the product. Presence of red color in the product is taken as evidence of tax evasion if the fuel is sold as taxed commercial diesel.
In many cases, however, it is desirable that the marker material not be visible in the product. Markers that are not visibly discernible are termed "silent markers." Silent markers identify a product to an authorized tester. However, silent markers do not provide any visual indication of the identity of the product to the regular or non-authorized user. Silent markers must also be miscible with the fuel and should be difficult to remove (e.g., by ultrafiltration). Similarly, silent markers must be detectable by a subsequent manipulation of a sample from the product.
In order to detect the presence of a silent marker, many of the existing markers must be extracted by a chemical process. Typically, the chemical process includes shaking a sample of the product with a water-based reagent. The addition of a chemical agent to the water phase causes the extract to turn to a visibly distinct color. The depth of the color indicates the quantity of marker present in the sample. A laboratory measurement in a spectrometer indicates the concentration of marker present in the isolated sample. Comparing the measured concentration with the original concentration of marker in the fuel assists in the identification of the fuel.
In contrast, some silent markers are large organic molecules that either absorb or fluoresce in the near infrared to mark their presence in a fuel sample. U.S. Pat. No. 5,525,516 (Eastman Chemical), incorporated herein by reference, and German Patent DE4224301A1 (BASF) describe such markers. In U.S. Pat. No. 5,525,516, the presence of such a silent marker is detected by exposing the marker to near infrared radiation and then detecting emitted fluorescent light via a near infrared light detection element. Molecules or markers that are active in the near IR are large, complex, organic structures. Therefore, these markers are difficult and expensive to make. Furthermore, there are only a finite number of near infrared fluorescing molecules that can serve as silent markers, and many of these molecules are visually detectable. Thus, there are a limited number of expensive, hard-to-make near infrared, fluorescing molecules that can serve as silent markers.
In sum, few practical markers exist, and even fewer practical, silent markers exist. Furthermore, many silent markers are not user friendly in that a user must chemically manipulate a sample of the marked product to detect the marker. With the growing drive to prevent brand adulteration of fuel and the widening use of markers around the world for enforcement of taxation, more markers and an improved method of marking are needed.
The invention is next described in connection with certain embodiments; however, it will be clear to those skilled in the art of petroleum product marking that various modifications, additions and subtractions can be made to the described embodiments without departing from the spirit or scope of the invention.